A Submucosal Moderately Poor Differentiated Laryngeal Squamous Cell Carcinoma Presenting as a Thyroid Mass: A Report of a New Case

<b>Background:</b> Submucosal laryngeal carcinoma (SLC) is a rare subtype of transglottic laryngeal carcinoma (TLC) and usually originates from the center of the laryngeal ventricle. Nearly 70% of TLC cases are confined to the larynx and 30% show external laryngeal infiltrations. Early stage asymptomatic TLC usually shows occult lesions and tends to grow into lateral parapharyngeal space. <b>Case Summary:</b> We present an unusual case of submucosal moderately poor differentiated laryngeal squamous cell carcinoma (SCC) characterized by thyroid mass, hoarseness, and dyspnea as the main symptoms. In this case, a 60-year-old Chinese male was made a preliminary diagnosis of suspected thyroid carcinoma (TC) with laryngeal metastases to the cricoid cartilage. No laryngeal neoplasms were observed under nasopharyngo-fiberoscope. After giving 1-month therapy with anlotinib, the tumor lesion had minimal response while the patient insisted on surgical section to relieve dyspnea. Intraoperative frozen section biopsy confirmed that the tumor was moderately poor differentiated SCC of the larynx, and in this case, thyroid metastases might result in SLC penetration of cricothyroid membrane. <b>Conclusion:</b> SLC should be taken into consideration in the case of suspicious TC with laryngeal cartilage infiltration and subglottic area infiltration. Further coarse needle puncture or surgical biopsy should be carried out to clarify diagnosis to optimize treatment strategy.